Pseudohypercalcemia in an elderly patient with multiple myeloma: report of a case and review of literature.

Hypercalcemia, a common complication of multiple myeloma, is primarily caused by increased bone resorption. The increase in total calcium is usually associated with an increase in the ionized calcium (Ca(I)), and the hypercalcemia is frequently symptomatic. Rarely, pseudohypercalcemia in multiple myeloma is caused by binding of calcium to the abnormal immunoglobulin. In this setting, the Ca(I) is normal. We describe a 90-year-old woman with an IgA-k myeloma who had substantial increases in the total calcium but normal levels of Ca(I). Clinicians should recognize this unusual phenomenon to avoid unnecessary and potentially toxic therapy.